Abstract

Measurements were made of the dielectric constant along the ferroelectric axis εa, the spontaneous polarization Ps and the heat capacity cp of Rb2ZnCl4 crystals in the temperature range from −150°C to 150°C. The normal-incommensurate transition point determined as the peak position of cp lies at 30.1°C, which is about 6°C lower than the temperature for the maximum of εa. It was found that εa and Ps show a characteristic thermal hysteresis over a wide temperature range including the incommensurate-commensurate transition point (−80°C). The thermal hysteresis occurs even when heating and cooling runs are cycled within the incommensurate phase. The observed thermal hysteresis is understood if we assume that defects such as impurities act as obtacles to diffusion of discommensurations and prevent the crystal from reaching thermal equilibrium.